Order this Backer-On #9 x 2-1/4 in. Backer-On Serrated Flat Head Star Drive Cement Board Screws for delivery. Serrated head design for flush seating even at an angle. Star drive with T-25 bit provides StikfitTM for easy 1-handed installation and eliminates cam-outs. Serrated thread forms require less torque for faster installation. Patented sharp point offers immediate pick-up and eliminates the need to pre-drill. Patented design allows attaching close to edge on cement board, drastically reducing fractures or blow outs. Premium corrosion resistant finish. Use to attach cement board to wood or light gauge steel studs. Ideal for use in high moisture areas such as showers, backsplashes, countertops and floors. Conforms to ANSI A108.11 standards for cement board attachment. Best Screws And Nails For Drywall.